A healthy eye is has photosensitive retinal cells (e.g. rods and cones) which react to specific wavelengths of light to trigger nerve impulses. Complex interconnections among the retinal nerves assemble these impulses which are carried through the optic nerve to the visual centers of the brain, where they are interpreted. Certain forms of visual impairment are primarily attributable to a malfunction of the photosensitive retinal cells. In such cases, sight may be enhanced by a retinal prosthesis implanted in a patient's eye. Michelson (U.S. Pat. No. 4,628,933) and Chow (U.S. Pat. Nos. 5,016,633; 5,397,350; 5,556,423) teach a retinal implant, or implants, of essentially photoreceptors facing out of the eye toward the pupil, each with an electrode which can stimulate a bipolar, or similar, cell with an electrical impulse. This bipolar cell is acted upon by the electrical stimulus, to send appropriate nerve impulses essentially through the optic nerve, to the brain.
This invention is postulated as a necessary complement to this type of prosthesis, because the photoreceptors do not appear to be sensitive enough to the ordinary levels of light entering the eye in that not enough current is produced to sufficiently stimulate the retinal cells. Consequently, a light amplifier, or “helper” device would be needed. That device is the invention here described, which also includes special characteristic implants.
Furness, et al. teach a “virtual retinal display”, U.S. Pat. No. 5,659,327, where “The virtual retinal display . . . utilizes photon generation and manipulation to create a panoramic, high resolution, color virtual image that is projected directly onto the retina of the eye . . . there being no real or aerial image that is viewed via a mirror or optics.” Richard, et al. teach, U.S. Pat. No. 5,369,415, “ . . . a direct retinal scan display including the steps of providing a directed beam of light, modulating the beam of light to impress video information onto the beam of light, deflecting the beam in two orthogonal directions, providing a planar imager including an input for receiving a beam of light into the eye of an operator which involves a redirection diffractive optical element for creating a virtual image from the beam of light on the retina of the eye, and directing the beam of light scanned in two orthogonal directions and modulated into the input of the planar imager and the output of the planar imager into the eye of an operator.”
Sighted individuals can use these devices above for their intended uses. However, they appear unsuitable for use by blind individuals with implanted retinal prosthetics of the photoreceptor-electrode kind. It would seem that they do not provide enough light power. Moreover, light amplitude cannot be arbitrarily increased because according to Slinly and Wolbarscht, Safety with Lasers and Other Optical Sources, the retinal threshold damage is 0.4 Joules per square centimeter.